A device of the type indicated above has been previously proposed comprising an intracardiac catheter provided near its end with four elements for the transmission of ultrasonic waves, which elements are spaced equiangularly apart at 90.degree. intervals and which each have some directivity. With the aid of this catheter, it is possible to transmit ultransonic waves in four different directions and to determine the distance to the heart wall from the time interval between the excitation of the elements and the reception of the echo pulse. If the entire heart wall is to be scanned, the catheter must be rotated about is axis, a procedure which is difficult to realize. It will therefore be clear that, with this catheter, it is not possible at any moment to completely visualize moving cardiac structures, such as heart walls and heart valves, surrounding the catheter. In principle, it would be possible to determine the dimensions of the heart in a larger number of directions by providing the catheter with a larger number of elements.
Techniques for determining the distance from object in one of a larger number of directions around an ultrasonic source are known in themselves from Sonar (Bom, Lancee, Algemene inleiding tot de echocardiografie, Het Ingeniemsblad, No. 3, 1972, p. 3-6). The possibility of applying Sonar Techniques to a heart catheter has also been touched upon in a paper presented to the British Medical Ultrasonics Group, at Glasgow, Great-Britain, Dec. 10, 1971, (Bom, Lancee, Technical Developments in echocardiographic apparatus). However, the dimensioning of the ultrasonic equipment for Sonar is such that without difficulty it can be provided with a large number of elements.
In contrast to the situation with Sonar, however, the dimensions permissible for a catheter are in the order of magnitude of millimeters, thus limiting the number of directional elements at the frequencies used for diagnostic purposes.